|dc.description.abstract||To investigate the origin of red quasi-stellar objects (QSOs), we studied the color and physical properties of the QSOs selected from the Sloan Digital Sky Survey (SDSS) using both spectral and photometric information. We choose 1750 Å, 2200 Å, 3100 Å and 4000 Å mean flux density at rest frame to calculate the colors of QSOs. We defined ‘red QSOs’ and ‘typical QSOs’ with three different colors.
If the ‘red QSOs’ were due to dust extinction, they need Av = 0.2~0.8 to reach the definitions of ‘red QSOs’ in this study. We also investigate the red QSOs with the whole spectra of SDSS. Some extreme red QSOs defined in two different colors can be explained with dust extinction. There were 27/35 red QSOs, which had red colors defined with 1750Å, 2200Å and 3100Å band fluxes, could be explained with dust extinction. There were 133/154 red QSOs, which had two colors defined with 2200Å, 3100Å and 4000Å band fluxes, could be explained with dust extinction.
There is a clear boundary on the color-luminosity diagrams of the QSO. The blue and bright QSOs seem to be missed. We called this phenomenon ‘the missing blue QSOs’. It might be related to the central black hole mass of QSOs or accretion rates. However, we could not get a clear relation with a simple test of the data. The origin of the missing blue QSOs is still unclear.||en_US|